Substituent Effects on Transient, Carbodiimide-Induced Geometry Changes in Diphenic Acids

Nucleotide-induced conformational
changes in motor proteins are
key to many important cell functions. Inspired by this biological
behavior, we report a simple chemically fueled system that exhibits
carbodiimide-induced geometry changes. Bridging via transient anhydride
formation leads to a significant reduction of the twist about the
biaryl bond of substituted diphenic acids, giving a simple molecular
clamp. The kinetics are well-described by a simple mechanism, allowing
structure–property effects to be determined. The kinetic parameters
can be used to derive important characteristics of the system such
as the efficiencies (anhydride yields), maximum anhydride concentrations,
and overall lifetimes. Transient diphenic anhydrides tolerate steric
hindrance ortho to the biaryl bond but are significantly affected
by electronic effects, with electron-deficient substituents giving
lower yields, peak conversions, and lifetimes. The results provide
useful guidelines for the design of functional systems incorporating
diphenic acid units.